Modern buildings are designed to conserve energy and provide an optimal level of comfort. For example, in buildings using water systems for heating and cooling, the water/air heat exchangers have 3 valves connected in series to reach the objective of optimal control and energy conservation. DPCVs or Differential Pressure Control Valves are used to remove fluctuating system pressures. Flow Regulation valves enable system balancing. Comfort Controllers use two (2) Port Control valves which react to room thermostats. However, the design of these valves has a maximum force limit that, if surpassed, will damage the valve. Therefore, the force on the valve stem is an important limiting factor.
The two Port Control valves are proportionally moved to the desired opening positions by an proportional actuator which is controlled by a correction signal supplied by the central controller or the comfort controllers which obtain sensed signals from the room thermostat. To move the two port valve to a desired position, the valve actuator needs to provide sufficient force to move the stem of the valve.
There was never a requirement for a predetermined maximum allowable force on these valve stems operable on two Port Control valves since the construction of the valves could absorb forces much greater than the force generated by the actuator.
The most modern and efficient approach is to combine the functions of the DPCV, Flow Regulation, and 2 Port Control valves, into a single PICV or Pressure Independent Control Valve which (a) Reduces the number of valves; (b) Reduces installation time; (c) Reduces number of joints/potential leaks; (d) Simplifies selection, and (e) Simplifies commissioning of the entire system.
As an example for installations incorporating Fan Coil Units (FCU) or chilled beams, the PICV offers an excellent solution for control of water flow rates, and therefore comfort control and energy savings when used as part of a variable volume system. The only drawback to the combination of functionally of these three (3) different valves into one PICV valve is the narrow force band in which the PICV can operate. In other words, with too little force the valve actuator will not be able to move the valve stem and with too much force the valve actuator will destroy the special cartridge that makes the PICV operational.
Whereas normally constructed valve actuators are tested only for minimum force and can tolerate very high varying maximum force (for example, +/−80 N (Newtons)), from one actuator to the next, the PICV valves require control with variations from actuator to actuator not more than, for example, 10 N. Further, this valve actuator design must be done in a very economical basis for the applications mentioned above.
In connection with light duty valve actuators (less than 1100 N), manufacturers typically identify the minimum force required to use the valve said stem during operation. In the field, valve actuator and motors can vary +/−100 N from motor to motor. Within the valve actuator itself the force produced can vary +/−80 N depending on the place of travel in the actuator.
The intention of this invention is to provide a valve actuator with a force limiting device to be able to operate within the narrow operational force requirement of the PICV type Valve for 2 port or multiple port designs.